A liquefied natural gas (LNG) storage tank is used for storing or transporting liquefied natural gas (LNG) at an ultralow temperature of about −162° C., and is provided with two barriers (a first barrier and a second barrier) for sealing the LNG.
In addition, the LNG storage tank forms a heat-insulating layer using a heat-insulating board in which a heat-insulating member-protecting plate having a high compressive strength like plywood is combined with a heat-insulating member that is formed of a polyurethane foam material having low thermal conductivity between the first barrier and the second barrier and between the second barrier and an internal hull.
In this case, the first barrier of the LNG storage tank is required to provide high air-tightness because it directly contacts the LNG.
In the LNG storage tank, since a plurality of barrier sheets formed of a stainless steel material are bonded by welding to form the first barriers, the first barriers may undergo heat-shrinkage when contacting the ultra-low temperature LNG and thus welding portions thereof can be broken by thermal stress when the heat shrinkage occurs.
Because of such a problem, the first barriers have corrugated portions to have low in-plane stiffness.
When the heat-shrinkage occurs, the corrugated portions are deformed to a certain degree, thereby reducing the thermal stress at the welding portions.
Meanwhile, when the LNG storage tank in which the LNG is stored is transported by means of transportation such as a vessel and the like, movement can occur on a surface of the stored LNG by movements such as rolling, pitching, and the like of the vessel during transportation.
Such movement is referred to as sloshing, and the sloshing causes a large compressive force to be applied to the first barriers.
When the compressive force due to the sloshing exceeds yield strengths of the first barriers, the corrugated portions can be permanently deformed because they are the most vulnerable to deformation, thereby deteriorating safety of the first barriers.
Thus, the first barriers should not only maintain the low in-plane stiffness in response to the thermal shrinkage, but also have high pressure resistance performance in response to the compressive force due to the sloshing.
In order to improve the pressure resistance performance of the first barriers, the applicant of the present invention has disclosed, in Korean application No. 10-2008-0091085, a structure in which reinforcing members are installed under the corrugated portions of the first barriers.
However, such reinforcing members are not fixed to the corrugated portions of the first barrier, thereby making it difficult to install the reinforcing members under the corrugated portions of the first barrier.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.